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I had been running stock exhaust for years with a muffler delete section added. Over the last few years, where the welds were on the straight pipe section, rusted to the point that they weren't holding that section anymore and there were baseball sized holes in the pipe. Then last fall, the weld that held the tailpipe to that section broke and the section that went over the rear axle was dangling so I removed it. So for a while now I have been running straight pipe that terminated underneath the bed in front of the rear axle, sooting up the back half of the truck in the process.
This past weekend I got around to installing the 4 inch stainless steel turbo back system I got from Flow Pro. It went as well as anything in recent memory with this truck. A buddy and myself did it at his house in the garage in about an hour and 45 minutes start to finish, taking our time and having a few beers. The quality of the kit was fantastic. The fit was very good and it went together very easily. The hardest part was, as usual, the down pipe clamp and lining up the new 4inch down pipe.
The one thing I was a little disappointed in was I ordered the kit through my mechanic so he could make a little coin off the transaction even though I wasn't having him do the installation and when I ordered it, I paid extra for and it was supposed to have a muffler. The system I got had the "for race applications only" muffler delete section. Having run straight pipe for almost 9 years now, I was looking forward to it being a little quieter.
I know I am getting old, I can barely believe I just typed that. I spoke with my mechanic and he said Pro Flow was made aware of the error and they are going to ship the muffler section with their next order and in the mean time, I am running straight pipe again, but it is quieter because the exhaust isn't terminated under the front section of the bed.
Here are some pics, not great ones but, you all know what an exhaust looks like anyway.
Here is the delete section. It will be very easy to remove and replace, due to those nice clamps, as opposed to the standard exhaust clamps that tend to crush the pipes and if I think the truck is too quiet, I will swap the delete back in. Pay no attention to the rusty bed cross member in the upper right hand corner of this shot...
I installed the aluminzed version with the muffler on Forrest. It's a great kit and one of the key reasons for that aside from fitting well is the band clamps. The muffler makes it very quiet in the cab. Sounds good outside though. I will be interested to hear your impression as you're going from straight to muffled with the same exhaust I have.
I'm going with a muffler and either FTE or Aeroturbine resonator with my build. Looking hard at the flo pro setup. a lot cheaper than mrbp.
I've been under mine...looking for place for FTE resonator....it looks like right behind the crossmember is the closest to the engine I could place it.
The size difference in the down pipe was amazing. The stock down pipe is only 3 inch, while the stock exhaust is 3.5 inches. The new down pipe is 4 inch as well as the exhaust itself. It makes a big difference. I haven't towed with it, but I have to believe that it will make a difference in exhaust temps.
I remember having a very long discussion with the guy who started and owned Pinnacle Exhaust (before they went out of business). He had done a lot of design testing on the ideal down pipe sizing effort, and what he had learned was fascinating.
He said that in all their design studies and performance testing efforts on the 7.3, the ideal down pipe size was actually to NOT make a uniform 4" diameter pipe starting from the very beginning at the turbo. The ideal flow characteristics were achieved by starting out with 3.5" at the turbo outlet and only increasing to the 4" diameter about half way through the length of the down pipe. The flow dynamics are all about managing the combined effects of cooling and pressure drop in a more gradual basis. If you simply use a full 4" diameter at the beginning of the down pipe, the rapid expansion of gases out of the turbo into that 4" diameter pipe creates excessive turbulence, and you end up with the exhaust fighting itself immediately out of the turbo which reduces the dynamic flow velocity through the system.
Conversely, if you use a more gradual size increase, the gases expand in volume more gently and can then maintain what they refer to as laminar flow (straight line velocity with minimal turbulence). Laminar flow will allow reduce the actual pressure drop (velocity losses due to friction) and the end result is a steadier and faster flow velocity through the entire system.
Alas, though, Pinnacle is no more (at least I cannot find them), and we are now left with manufacturers who take the easiest production route of the simple one-sized 4-inch approach on the down pipe. It's not the most efficient flow design, but is the more cost-effective manufacturing approach because it eliminates two weld points and any potential alignment issues while performing those two welds.
I installed the Flo-Pro on my 6.0L, I like it. - I was shocked at the price here locally. The shop's charge included installation which was cheaper than I could buy the MBRP setup for and install it myself. I like the beefy band clamps they send with it, just keep an eye on the one connecting the last section Jason. That bugger loosened up twice on me.
I remember having a very long discussion with the guy who started and owned Pinnacle Exhaust (before they went out of business). He had done a lot of design testing on the ideal down pipe sizing effort, and what he had learned was fascinating.
He said that in all their design studies and performance testing efforts on the 7.3, the ideal down pipe size was actually to NOT make a uniform 4" diameter pipe starting from the very beginning at the turbo. The ideal flow characteristics were achieved by starting out with 3.5" at the turbo outlet and only increasing to the 4" diameter about half way through the length of the down pipe. The flow dynamics are all about managing the combined effects of cooling and pressure drop in a more gradual basis. If you simply use a full 4" diameter at the beginning of the down pipe, the rapid expansion of gases out of the turbo into that 4" diameter pipe creates excessive turbulence, and you end up with the exhaust fighting itself immediately out of the turbo which reduces the dynamic flow velocity through the system.........
I've read about some 6.0L owners experience a bit of turbo lag with a full 4" downpipe.......I haven't really noticed a difference - except in the EGT's & sound. But if you do have issues and it bothers you - they sell a 3 1/2" downpipe.
I wonder how much the fact that I have a 38R versus a stock 38 effects the flow characteristics of the 3.5inch step down then 4inch, versus just the straight 4inch?
I would say that it has to have an effect to some degree, Jason. My gut feeling is that it really depends on how much air is actually being pushed by the turbo. I know that the 38R has more air-moving capacity, but I don't know to what degree you are actually getting that additional air flow as you drive normally.
The principle goes like this... the more extreme the change in pressure, the more extreme the degree of turbulence. That being said, your 38R can handle the full-length 4" down pipe better than a stock turbo (i.e. it has the potential to experience less turbulence-driven friction losses), but only when it is actually flowing more air than the stock turbo.
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I spoke with my mechanic and he said Pro Flow was made aware of the error and they are going to ship the muffler section with their next order and in the mean time, I am running straight pipe again, but it is quieter because the exhaust isn't terminated under the front section of the bed. 
